This type of scan also involves the use of radiation. In this case, a radio isotope is injected into your blood. The isotope which is attached to a component of bone tissue which is taken up by active bony tissue is then incorporated into the bone. You then sit in front of a camera at various times following the injection to detect where areas of increased activity are occurring. Bone scanning is a very sensitive but non-specific imaging modality. It will pick up areas of increased turnover, but does not necessarily tell you the cause of the increased turnover. The most common cause of bone turnover is degenerative disease (osteoarthritis). As osteoarthritis starts to develop, the affected bones increase their activity for various reasons. Into these areas of increased activity the radio isotope marker will be taken up and these will be shown up as 'hot spots'.

Bone scanning is commonly used to detect the spread of tumours in the body. It is a modality that will allow imaging of the whole skeleton at no extra increased radiation dose. It is also used for detecting degenerative disease. In the case of a person with what appears to be single compartment arthritis within the knee joint, who may be a candidate for a single compartment minimally invasive joint replacement, a bone scan be used to confirm the diagnosis. If the bone scan shows that the activity is truly limited to one compartment, this lends further support to the patients' potential suitability for a partial joint replacement, as opposed to a joint replacement, with the added advantages of the former.
There are variations of bone scans such as three-phase bone scanning which allows differentiation of increase uptake due to increased blood flow, increased activity in soft tissues or increased activity in bone. With a three-phase bone scan, a first picture is taken within a few seconds of injecting the dye over the particular area of interest such as the knee joint. A second image is taken half an hour or so later. This will highlight the soft tissue. Final delayed images are then taken three to four hours after the injection to highlight the bone. Sometimes further delayed images can be taken 24 hours later for more information.

Another variation on bone scanning is a white cell labelled scan. In this case, a sample of the patient's blood is withdrawn and the white cells are labelled with a radio isotope. The blood is then injected back into the patient and the scanning protocols are followed. In this case, any areas of increased uptake will be due to concentration of white cells in the body. This is commonly used to diagnosis bone infections, especially around total joint replacements. This type of scan has now moved on and is now done using monoclonal antibodies to the white cells so that a sample of the patient's blood does not have to be taken and the radio isotope is attached to an antibody to the white cells, and therefore when injected into the body, the antibody and the white cells will join together and so the white cells will be marked in this manner.

Last updated 08/04/2007

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